Low-Energy Irradiation Damage in Single-Walled Carbon Nanotubes

Abstract

We show that low-energy (20 eV–20 keV) electron or photon irradiation extinguishes the characteristic physical and chemical properties of single-walled carbon nanotubes, indicating that the irradiation damages the nanotubes. The irradiation-induced defects convert the electric properties of metallic SWNTs to semiconducting, and the nominal bandgap can be tuned simply by the irradiation dose. The defects also have the following interesting properties. The damage and recovery are reversible, indicating that the number of carbon atoms is preserved. The damage and recovery strongly depend on the diameter, suggesting that the damage is prominent in a rolled up graphene sheet, but not in a planar one. The activation energy of the defect healing is so small, depending on the diameter, that the defects can be healed even at room temperature or below.

Origin of the Electric Property Change of a Single-Wall Carbon Nanotube Caused by Low-Energy Irradiation: Defects or Substrate Charging?

“…2 and 3 are consistent with each other. They are also consistent with previous studies using on-substrate SWNT devices [5][6][7][8]. Theoretical calculations have shown that a high electric field of ∼1 V·nm −1 barely opens a band gap of several ten millielectron volts.…”

“…A moderate irradiation can convert the room temperature electric properties of a metallic SWNT to semiconducting [4]. An intensive irradiation finally makes a SWNT almost insulating [5][6][7][8]. The decreased conductivity with the irradiation, as well as the degraded Raman and PL spectra, can recover reversibly by annealing [1,3,6] or applying a high bias to the SWNTs [7,8].…”

“…Although the irradiation-induced conductivity decreases in a SWNT and its recovery have been experimentally well established [5][6][7][8], the origin of the conductivity decrease is still controversial. We have reported that the irradiation-induced physical property changes are caused by defects created by the irradiation (low-energy irradiation damage) [6].…”

“…We have reported that the irradiation-induced physical property changes are caused by defects created by the irradiation (low-energy irradiation damage) [6]. The number of carbon atoms should be preserved during the defect formation in order to account for the fact that the defect recovers reversibly.…”

“…The previous experiments were performed using conventional SWNT devices, in which the SWNTs were lying on a gate dielectric SiO 2 layer [5][6][7][8]. In this geometry, the SWNT might be strongly affected by charging of the dielectric in the vicinity of it, considering that the electric field formed by a point charge is inversely proportional to the square of the distance.…”